A general stitching technique for attaching a zipper tape f.sub.t to a garment W will be explained.
This technique is best understood by referring to FIG. 4. When stitching lines S.sub.1, S.sub.2 are finished, some kind of a lever is required to turn over flap W.sub.f such that stitch line S.sub.3 will be exposed during stitching.
One conventional way of turning over the flap will be explained with reference to FIGS. 5A and 5B. When the stitch lines S.sub.1, S.sub.2 (FIG. 4) are finished, rod a is pulled in the direction of arrow A in FIG. 5B by some driving source (not shown), so that link b pivoted to rod a rotates counter-clockwise around shaft c and consequently lever d rotates clockwise around shaft e. Since shaft e is slidably inserted in the oblong hole d.sub.1 provided at the lever d, the tip d.sub.2 of lever d traces a parabolic curve E.sub.p as shown in FIG. 5b.
In a conventional flap-turning apparatus, the tip d.sub.2 rotates around shaft e as shown in FIG. 6.
The radius of rotation when the tip d.sub.2 moves to its lowest position at O is R.sub.o.
The radius of rotation when the tip d.sub.2 is positioned as shown in FIG. 6 is R.sub.1. The rotating radius decreases as the tip d.sub.2 moves laterally, so the tip d.sub.2 tends to take an unnecessarily high position when it moves laterally. Because of this, when the garment material is soft, the flap W.sub.f tends to escape from the tip d.sub.2.